Study on the Segmentation of the Right Posterior Sector of the Liver

Background The border between segments VI and VII of the right posterior sector of the liver is controversial owing to lack of anatomical landmarks. This study aimed to examine the segmentation of the right posterior sector. Methods Using three-dimensional software, ramification type of the right posterior portal vein (RPPV) was analysed in 100 patients. Results A bow-shaped anatomy, in which the RPPV exhibits a downward convex bow shape with several ramifications, was found in 50 patients. A bifurcation anatomy, in which the RPPV bifurcates into the cranial and caudal branches, was observed in 45 patients. In the bow-shaped anatomy, setting the segmentation was difficult due to lack of definite landmarks; thus, the downward portal branches were determined as segment VI branches, while horizontal and upward branches were determined as segment VII branches. In the bow-shaped anatomy, the incidence of full exposure of a thick branch of the right hepatic vein on virtual transection surface was 60.0%, while in the bifurcation anatomy, it was only 11.1%. No relations were observed between RPPV anatomy and main PV/right hepatic vein anatomy. The volumes of segments VI and VII were equal in both the bow-shaped and bifurcation anatomy. Conclusions The bow-shaped and bifurcation types are commonly observed in RPPV anatomy. In the bifurcation anatomy, the right posterior sector is divided into segments VI and VII. In the bow-shaped anatomy, setting the segmentation was difficult, thus it may be compelled to be arbitrarily determined.